Refining of fatty oils



Oct. 10, 1961 A. u. AYRES 0 REFINING OF FATTY OILS Filed Feb. 27, 1958 3Sheets-Sheet l Fig.

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INVENTOR. l4 ARTHUR U. AYRES BYW ATTORNEY Oct. 10, 1961 A. u. AYRES3,004,050 I REFINING OF FATTY OILS Filed Feb. 27, 1958 5 Sheets-Sheet 2INVENTOR. ARTHUR u. AYRES MUM ATIORNEY United States Patent 3,004,050REFINING 0F FATTY OILS Arthur U. Ayres, Philadelphia, Pa., assignor toThe Sharples Corporation, a corporation of Delaware Filed Feb. 27, 1958,Ser. No. 718,034 14 Claims. -(Cl. 260-425) This invention pertains tothe refining of fatty oils (cg. glyceride oils), and more particularlyto the refining of vegetable and animal oils, such as cottonseed oil,soya bean oil, peanut oil, corn oil, sunflower seed oil, sesame oil,rape seed oil, cocoanut oil, babassu oil, palm oil, palm kernel oil,linseed oil, tallow, lard, grease, fish oil, whale oil, etc.

Fatty oils are ordinarily refined by treating the same with an aqueousalkaline reagent, such as sodium carbonate and/or sodium hydroxide. Thisis followed by the separation of the refined oil from the aqueous phase,the latter containing reaction products and/ or impurities such assoapstock, gums, and/ or color bodies. The purpose of such refining isto neutralize and remove free fatty acids, to remove gums, to removecolor bodies and/or to otherwise improve the quality of the oil.

Such refining, particularly when the purpose is to remove free fattyacids, is frequently followed by a second refining known in the art asrerefining. The purpose of rerefining is to further improve the qualityof the oil, largely by way of removal of color bodies, for which areagent comprised of aqueous caustic soda is well suited.

The use of a rerefining step is generally accepted practice when aqueoussodium carbonate is employed as the reagent for neutralizing free fattyacids in the initial refining, for sodium carbonate is rather deficientas a reagent for removing color bodies. The use of a rerefining step isalso beneficial in many instances, depending on the source and/or typeof the crude oil, when the initial refining is conducted Withstoichiometric or near stoichiornetric proportions, based on free fattyacid present, of caustic soda as the refining reagent.

In any event, the residue of free fatty acids remaining in the fatty oilafter initial refining with an alkaline reagent to remove free fattyacids is very low, e.g. below .25%. Fatty oils so refined also are lowin materials commonly referred to as gums, e.g. phosphatides,proteinaceous materials, resins, etc. Fatty oils which have beendegumrned otherwise than by treatment with a reagent to remove freefatty acids also are low in gums. Also certain fatty oils are initiallylow in free fatty acids, e.g. below 1%.

In the treatment of such fatty oils which are low in free fatty acidsand/o1- gums, whether in such state naturally or as a result of priorprocessing, it is common practice to employ a reagent, such as aqueouscaustic soda, to improve the quality of the oil, eg by reduction in freefatty acids and/or color or otherwise. In such practice a small amountof soapstock is usually formed, whether by reduction in free fattyacids, or by saponification of a small amount of neutral oil, or both,and the aqueous caustic soda reagent solutions employed are frequentlyof such concentration as to cause the soapstock formed to be salted on'from the aqueous reagent phase, or to otherwise appear in whole or inpart in the form of a third phase separate from the oil and the aqueousreagent phase. The result is that the soapstock, being of a densityintermediate that of the fatty oil and that of the aqueous phase, tendsto be dischargedfrom the centrifuge along with the fatty oil. This isbecause the aqueous phase, being of a density greater than that of thesoapstock phase, forms a layer in the bowl in a position radiallyoutwardly from the soapstock layer, and thus interferes with the properdischarge of the soapstock layer from the bowl as a heavierphase. As aresult,

at least a part of the soapstock is forced to discharge from the bowl asa lighter phase, i.e. along with the oil, thus defeating the purpose ofthe operation, which is to separate both soapstock and aqueous reagentphase from the oil.

This condition may be alleviated, at least to some extent, by theseparate feed of water into the peripheral zone of the bowl to reducethe concentration of caustic soda in the aqueous phase, with consequentreduction in its density, ideally to a point where the density of theaqueous phase becomes the same .as that of the soap stock phase. Underideal or near ideal conditions, both phases then are discharged from thebowl together, and separately from the oil. The dilution of the aqueousphase, however, results in the formation of a certain amount ofoil-containing aqueous emulsion which is discharged from the bowl alongwith the soapstock and aqueous phases, with consequent loss in oil.

Another source of difliculty resides in the fact that the capacity ofthe soapstock phase to retain aqueous reagent phase, either by solutionor entrainment, varies not only between different oils, but also for anygiven individual oil depending in large measure on its gum content. Evenduring a given run there may be variations to the extent that a separateaqueous layer may form only sporadically, or may disappear sporadically.In any event, it is diflicult to continuously centrifuga-lly separate byliquid balance an aqueous reagent phase as a layer separate from thesoapstock layer, and to continuously discharge the same from the bowl,e.g. over a weir.

After extensive experimentation, I have discovered and perfected amethod for the refining of fatty oils wherein the aqueous phase, if,when and to the extent occurring as a layer separate from the soapstocklayer, is separated and separately discharged from the centrifugal bowl,while leaving the oil and soapstock layers in desired hydrostaticbalance.

Further features of the invention will become ap parent to personsskilled in the art upon becoming familiar herewith, and as thespecificationproceeds, and upon reference to the drawings in which:

FIGURE 1 is a vertical section, shown broken, illustrating apparatusembodying and useful in the practice of the invention;

FIGURE 2 is a section taken generally on line 22 of FIGURE 1, withportions removed for better illustration; and

FIGURE 3 is an enlargement of a portion of .FIG- URE. 1.

Referring now more particularly to the drawings, the centrifuge rotor10' is shown provided with an inlet feed boss 11 which is surrounded bya guide bushing assembly or drag 12. The guide bushing assembly 12 issecured in position on a base 13 which also carries a feed nozzle 14through which the reaction mass is continuously fed into the centrifugerotor 10.

In the apparatus as illustrated, an auxiliary feed nozzle 15 also issecured to the base 13, and surrounds the feed nozzle 14, and feednozzle 14 is shown provided with a circumferential head 16, the purposeof whichis to defiect outwardly against the inner wall of boss 11 anyliquid fed into the bowl through the'nozzle 15 in the practice of amodification of the inventionto behereinafter more particularlydescribed. 7

The lower end 17 of rotor "10 is provided .with a cylindrical flange 18positioned interiorly of the rotor. The

upper end of flange 18 forms a seat for a flange 20 of i a feeddirecting member 19 shown with aconicalbase portion. Member 19 may besecured in position on flange slots illustrated at 21, in order toafford outlets from 3 space between the member 19 and the innerperipheral bottom portion of the rotor for liquid fed into and passingupwardly and outwardly through such space.

Member 19, as shown, is provided on its inner conical surface with aplurality of circumferentially spaced radially extending vanes or fins28, and similarly on its outer conical surface with a plurality ofcircumferentially spaced radially extending vanes or fins 30. The fins28 extend inwardly toward feed opening 29 in the lowermost part of themember 19. Pins 30 extend from the outer surface of the member 19 to theinner surface of the lower end 17 of the rotor.

The construction so far particularly described may be regarded as moreor less conventional, and well-known.

Referring now to the upper part of rotor 10, at 31 is shown a rotor topwhich threadedly engages the upper interior of rotor as illustrated at32. Rotor top 31 includes an upwardly extending center portion 33 shownprovided with threads 34 for engagement by a nut on an overhead drivingspindle, not shown.

An annular member 35 threadedly engages rotor top 31 as illustrated at36, and is provided with an upwardly extending cylindrical portion 37which is threadedly engaged by a ring dam nut 38 as illustrated at 39,ring darn 42 being secured in position between cylindrical portion 37and ring dam nut 38.

Member 35 also is provided with an annular recessed portion 43 in whichis positioned an annular resilient valve member 44 shown associated witha plurality of circumferentially spaced vertical outlet channels 45milled into the interior wall of rotor 10.

In the operation of the apparatus shown in the drawings. a stream of thereaction mass is projected through nozzle 14 up into rotor 10 throughfeed opening 29, and is brought up to rotational speed with theassistance of fins 28, and circumferentially spaced radially extendingvanes 27. By virtue of centrifugal force, the reaction mass is separatedinto layers arranged in order of decreasing density in a radially inwarddirection from the interior peripheral wall of rotor 10.

In the following particular description which is by way of example, itwill be assumed that the reaction mixture is comprised of fatty oil,soapstock and aqueous caustic soda having a density greater than that ofthe soapstock.

Under the influence of centrifugal force, the aqueous electrolyte phase,being the heaviest phase, builds up on the interior wall of rotor :10,and flows toward annular recess 43, through a plurality ofcircumferentially spaced channels 40 in rotor top 31.

Annular valve member 44 is so chosen as to have a density intermediatethat of the soapstock phase and the aqueous electrolyte phase, and maybe of any suitable resilient material, such as rubber, natural orsynthetic, capable of increasing and decreasing in diameter, i.e. inradial distance from the axis of rotation, under the applied conditionspresent.

Valve member 44 is conveniently, though not necessarily, circular incross section, and its density may be varied to suit requirements by anymeans known in the art, e.g. ranging all the way from being made hollowto being loaded with various powdered substances, including metals,which may be incorporated in the rubber itself, or placed in a hollowinterior, or built in as a core, as will be readily understood bypersons skilled in the art.

It will be understood that when rotor 10 is empty, or when the aqueouselectrolyte phase does not form a layer separate from the soapstock,annular valve member 44 is expanded in radius, i.e. increased incircumference, by the applied centrifugal force so 'as to close verticaloutlet channels 45, for the density of member 44 is so chosen as to begreater than that of the soapstock layer.

Upon the appearance, however, of a third layer comprised of aqueouselectrolyte which, under the conditions assumed above, is of greaterdensity than the valve member 44, such aqueous electrolyte layer willflow upwardly along the interior wall of rotor 10 into annular recess43, whereupon annular valve member 44 will decrease in radius (i.e. incircumference) by virtue of floating in, or, in other WOIdS, beingdisplaced inwardly by, the heavier aqueous electrolyte layer whichescapes from the bowl through outlet channels 45.

Thus as long as an aqueous electrolyte layer is present in the rotor, itwill be discharged from the rotor through channels 45. Soapstock, on theother hand, will not be discharged through channels 45, for when anaqueous electrolyte layer is not present, channels 45 are closed byvirtue of the radial expansion of circumferential valve member 44 due tocentrifugal force, such expansion being possible in the presence ofsoapstock only, for valve member 44 is of greater density than thesoapstock.

From the foregoing it will be seen that when an aqueous electrolytelayer is present in rotor 10, irrespective of the manner in which it mayoccur, e.g. intermittently and/or varying in volume, it is carried offfrom the rotor 10 without interfering with the separation of soapstockfrom oil.

Oil and soapstoek are separated from each other in rotor 10, and aredischarged therefrom, in any desired manner.

As illustrated, rotor top 31 is provided with a conventional dividingdisc 46, around the inner circumferential edge 47 of which the separatedoil escapes upwardly, and around the outer circumferential edge 48 ofwhich the soapstock escapes upwardly.

The oil flows upwardly through a plurality of circumferentially spacedcircular channels 49 in rotor top 31, and into a plurality ofcircumferentially spaced channels 52 formed between longitudinal grooves53 in portion 33 and a sleeve 54 surrounding portion 33. The oil escapesover upper edge 55 of sleeve 54, and is collected in any convenientmanner such as by use of a rotor cover, not shown. Sleeve 54 may beattached to rotor top 31 in any desired manner, such as by welding.

Separated soapstock escapes upwardly around the circumferential edge 48of disc 46, and passes upwardly through circumferentially spacedchannels 56, area 57, and over the inner circumferential edge of ringdam 42, escaping outwardly through a plurality of circumferentiallyspaced outlet ports 58. As shown, the soapstock, on escaping from ports58, is deflected downwardly by hood 59, and may be collected along withaqueous electrolyte escaping through channels 45, in any suitable mannersuch as by the use of a rotor cover, not shown.

On the other hand, soapstock and aqueous electrolyte may be collectedseparately, if desired, as will be obvrous.

From the foregoing particular description it will be seen that, in thepractice of the invention, disturbances in the separation of soapstockfrom the oil due to the formation of a third layer comprised of aqueouselectrolyte, are eliminated, for if, when and as such aqueouselectrolyte layer forms, it is automatically and selectively removedfrom the zone of centrifugal separation through outlets separate fromthose for the discharge of oil and soapstock, thus permitting theseparation of soapstock from the oil to proceed in a normal way.

Priming of the centrifuge bowl upon start-up may be effected in anydesired or customary manner, in the present instance, preferably with aliquid of lower specific gravity than valve member 44, so as to keepchannels 45 closed during priming and to cause priming liquid todischarge over ring dam 42, as will be well understood by personsskilled in the art. Any suitable priming liquid may be employed, e.g.water, or an aqueous solution of electrolyte, such as of caustic soda orsodium carbonate.

As is well known in the art, the ease with which soapstock may bedischarged from a centrifugal rotor may vary widely from oil to oil andwith the conditions under which the oil is refined. Certain conditionsof refining, for instance, may reduce the fluidity of the soapstockquite materially. Moreover, the tendency of soapstock to stick to therotor wall also may vary from oil to oil and with the conditions ofrefining. In overcoming such difficulties, the present invention lendsitself ideally to the floating of the soapstock layer through the rotoron the surface of a heavier aqueous electrolyte layer, withoutinterfering with the separation of the soapstock from the oil by liquidbalance under the conditions employed in the zone of centrifugation, orthe discharge of the separated oil and soapstock layers from the rotor.Such floating of the soapstock layer on a heaviest aqueous electrolytelayer takes place in the practice of the invention whenever suchheaviest layer appears.

To assist in such discharge of soapstock from the rofor, a suitableauxiliary liquid of higher density than the soapstock, such as aqueouselectrolyte, may be passed upwardly through the annular space affordedbetween the nozzle and the nozzle 14 shown in FIGURE 1 of the drawings.This liquid impinges against the bead 16 formed on the nozzle 14 and isdeflected into contact with the inner wall of the boss 11 of the rotor10. The centrifugal force .generated by the rotation of the rotor 10causes the liquid to cling to this surface and to flow upwardly into thespace occupied by the radially extending fins 30. Pins 30 bring theliquid up to the speed of the rotor, and the liquid is impelledoutwardly through openings 21 under the influence of centrifugal force.Liquid impelled through the opening 21 flows upwardly along the innerwall of the rotor 10, thus forming a continuously moving liquid layerupon which the soapstock floats as it passes upwardly through the rotor.Sticking of the soapstock to the interior wall of the bowl and/ orpacking of the soapstock thereon are thus avoided.

The flotation liquid, being of higher density than the soapstock, isdischarged from the rotor through channels 45, the same as the aqueouselectrolyte layer is discharged when formed in the rotor as aboveparticularly described. Rubber ring or valve member 44 is, of course,chosen as to density to permit the discharge of the flotation liquid,but not of soapstock.

When the refining or rerefining is under conditions,

eg. including the source of the oil, such that a third layer comprisedof aqueous electrolyte is formed, or is likely to form, in the rotor,such as intermittently or continuously, the flotation liquid, ifemployed, is preferably though not necessarily of the same or similardensity as such aqueous electrolyte layer, and preferably though notnecessarily also is miscible therewith.

However, it is conceivable that, even though water has a densityslightly less than that of the usual soapstock, it might be fed into therotor as a flotation liquid when the formation of a separate layer ofaqueous electrolyte phase is assured, whereupon the water may merely mixwith the latterlayer to increase its volume with some de crease indensity, but preferably not closely approaching that of the soapstock,in order that valve member 44 may function in its intended manner.

Onn the other hand, aqueouscaustic soda and/or aqueous solutions of itssalts, such as of sodium carbonate or of sodium sulfate, or aqueoussolutions of any other suitable electrolyte, may be employed as theflotation liquid, if of higher density than soapstock, or if capable ofmixing with separated aqueous electrolyte to form a final flotationliquid of higher density than the soapstock, so as to make possible itsselective discharge from the rotor through the channels 45.

The following examples are given by way of illustration and not oflimitation.

Example I Degummed soya bean oil having a free fatty acid content of0.25% by weight was continuously mixed at a rate of 2500=pounds per hourwith 1.42% of its volume of aqueous caustic soda of 14 B. ata-temperature of F. The stream of mixed oil and aqueous caustic soda wasthen heated to F. and the stream was then centrifu'gally separated in acentrifuge having a rotor of the type shown in the drawings. A separatelayer of aqueous caustic soda began to form immediately in the rotor,and it was discharged peripherally therefrom, that is through channelssimilar to the channels 45. The soapstock was discharged over a ring damcorresponding to ring dam 42. A composite sample of the soapstock uponanalysis showed that it was of very low oil content, namely 2.04% byweight on a dry basis. The separated oil was bright throughout the runshowing that it was extremely low in soap content.

Example 2 Degummed soy-a bean oil having a free fatty acid content of0.45% by weight was continuously mixed at a rate of 2500 pounds per hourwith 2.68% of its volume of aqueous caustic soda of 12 B. at atemperature of 80 F. The stream of mixed oil and aqueous caustic sodawas then heated to 140 F., and the stream was then subjected tocentrifugal separation in a centrifuge having a rotor similar to therotor shown in the drawings, but with valve member 44 and channels 45omitted. There was. no discharge of separated heavy component for about20 minutes, whereupon soapstock (a composite heavy layer) began to bedischarged. The-separated oil was bright initially and relatively soapfree, but gradually became'more and more muddy with entrained soap. Inabout '35 minutes after the run started there was a sudden heavydischarge of soapstock, whereupon the discharged oil cleared up andbecame bright again. A number of such surges or sudden heavy dischargesof soapstock occurred with similar variations in the character of theseparated oil. A composite sample of the soapstock was analyzed, andshowed an oil content of 10.6% by weight on a dry basis. A compositesample of the refined oil showed that it was relatively high in soapcontent.

Example 3 In an efiort to rectify the unsatisfactory refining conditionsexemplified in Example 2, degummed soya bean oil having a free fattyacid content of 0.66% by weight was continuously mixed at a rate of 2500pounds per hour omitted. 7.5% by volume of water, based on the total fvolume of the reaction mass, was fed into the rotor of the centrifugethrough a feed nozzle having a construction and arrangement similar tothat disclosed at 15 in FIG-- URE 1 of the drawings, the water beingcontinuously deposited on the inner peripheral surface of the rotorthrough discharge orifices similar to slots 21. The action of the water,either by dilution of separated aqueous electrolyte and/or solution ofsoapstock, caused a uniform discharge of soapstock (composite heavycomponent) from the rotor, and the discharged oil was continuouslyrelatively soap free. Analysis of a composite sample of the soapstock,however, showed that it contained 29.4% of oil on a dry basis, whichrepresents a rather high loss in oil.

From the foregoing description it will be seen that the annular edge 47operates as a weir over which the lightest layer, e.g. refined vegetableoil, is discharged. It also will be seen that annular edge 47 controlsthe depth of liquid in the bowl, for it is not possible for liquid tobuild up in the bowl between the axis of rotationand the annular edge47.

The annular inner edge of ring dam 42 also operates as a weir over whichthe next heavier layer, i.e. the layer of intermediate specific gravityor density, e.g. soapstock, is discharged from the bowl. The radialdistance from the axis of rotation to the annular inner edge of ring dam42 controls the radial position of the dividing line or interface in thebowls separatory space between the lighest layer and the next heavierlayer. The radial position of such interface is made adjustable bymaking ring dam 42 interchangeable, and providing a variety of ring damswith annular inner edges of different radial distances from the axis ofrotation. In any event, such interface is made to fall between annularedge 47 and annular edge 48 when the bowl is in operation. For any givensize of ring dam 42, the radial position of the interface or dividingline between the lightest layer and the next heavier layer is dependentupon their relative specific gravities.

In the case of the refining or rerefining of fatty oils, it is customaryto select a ring dam 42 with the radial distance from the axis ofrotation to its inner operative edge such as to bring the interface ordividing line between the lightest and next heavier layers as close toannular edge 48 as is practicable, without possible loss of oil overweir 48 due to possible variations in conditions within the bowl. Thepurpose is to keep as large a volume of oil in the bowl as is reasonablypossible during separation, thus increasing the resident time duringwhich any portion of the oil is undergoing treatment for the separationof reaction products and reagent therefrom. The dividing line orinterface, however, may occupy any other position between annular edges47 and 48, as desired.

It is the disturbance of the hydrostatic balance between the lighter andnext heavier layers due to the appearance of a third layer, whetherintermittent or continual, that has heretofore presented a major problemin the refining of fatty oils, and particularly fatty oils of low freefatty acid and/or gum content, whether previously refined or not.

It is the removal of the heaviest layer from the bowl, as, if and whenit appears, that produces the new and unexpected results which fiow fromthe practice of the invention, for it is by effecting such removal ofthe heaviest layer that the desired hydrostatic balance between thelighter and the next heavier layers is maintained in undisturbedcondition. Since the heaviest layer may appear only intermittently, andmay vary considerably in volume, or if appearing continuously, may stillvary in volume during the separation, it is by the discharge of thisheaviest layer from the periphery of the bowl under control ofdifierence in specific gravities, that makes possible the desired highlyefficient separation of refined oil from reaction products and reagent.

While the invention has been described more particularly in connectionwith the rerefining of fatty oils, it is to be understood that it isapplicable to the initial refining of fatty oils under conditions suchthat a third layer of aqueous electrolyte is likely to appear. Alsowhile the appearance of a third layer comprised of aqueous electrolyteoccurs more often when caustic soda is employed as the alkaline refiningagent, the same situation is capable of occurring when other alkalinerefining reagents, such as sodium carbonate, are employed in excess.

In the practice of the invention, the concentration of alkaline refiningreagent in the aqueous solution employed for refining is not critical,for the concentrations normally employed vary widely from plant to plantand are such as to cause the appearance of a third layer in the bowl, ifthe aqueous reagent solution is employed in sufiicient excess to createthis condition. It may be expected, however, that with the samepercentage excess of aqueous refining solution over that required toneutralize free fatty acids, the appearance during the separation of athird layer is more likely to occur with aqueous solutions of higherBaum. Generally speaking, such third layer does not appear when thealkaline refining agent is substantially depleted during the treatment,e.g. in the case of aqueous caustic soda, to below a specific gravityequivalent to that of 12 Baum.

The temperature at which the process is practiced also is not critical,for the invention is operable irrespective of the temperature conditionsemployed, the latter being a matter of choice and judgment of theoperator. Temperature conditions employed in refiningfatty oils cover awide range as shown by the literature. Usually, however, they fallbetween C. and 200 C.

It will be understood that the invention provides a safety measureguarding against disturbing the hydrostatic balance between the fattyoil and soapstock or other reaction products by the possible appearanceof a third layer comprised of aqueous electrolyte.

While the valve member 44 has been more particularly described as arubber ring, this is by way of illustration, for it will be understoodthat valve member 44 may have any other suitable configuration or shape,for example, that of a sphere movable in a correspondingly shapedsocket, or otherwise. Also valve member 44 may be of any other suitablematerial of appropriate spec fic gravity intermediate that of theheavier and heaviest layers.

Moreover, while the centrifuge bowl has been illustrated for conveniencein the drawings as being of tubular shape, and as having wings servingas an acceleratlngdecelerating device, it is to be understood that thecentrifuge bowl may have any other configuration and constructionwithout departing from the spirit of the invention. Thus the inventionis equally adaptable to what is known as the disc-type bowl, and tobowls of any other type.

Having described my invention, it is to be understood that this is byway of illustration, and that changes, omissions, additions,substitutions and/or other modifications may be made without departingfrom the spirit thereof. Accordingly it is intended that the patentshall cover by suitable expression in the claims the various features ofpatentable novelty that reside in the invention.

I claim:

1. In the refining of fatty oil wherein aqueous alkaline reagent isadmixed with the oil in concentration and quantity such that uponsubjecting the reaction mass to centrifugation for the separation ofreaction products and reagent from the refined oil three layers areformed, the lighest layer being of oil, the next heavier layer being ofreaction products admixed with reagent, and the heaviest layer being ofreagent, the steps which comprise maintaining in the zone ofcentrifugation a balanced relationship between the oil layer and thereaction product layer dependent upon their specific gravities, andseparately discharging outwardly from the periphery of said zone ofcentrifugation the reagent layer as rapidly as it is formed.

2. The process of claim 1 wherein the alkaline reagent is caustic soda.

3. The process of claim 2 wherein the reaction products comprisesoapstock.

4. The process of claim 3 wherein the fatty oil is vegetable oil.

5. In a process for the refining of vegetable oil which comprisesadmixing aqueous caustic soda with the oil in concentration and quantitysuch that upon subjecting the reaction mass to centrifugation for theseparation of the refined oil from reaction products and reagent thereis a tendency for the reagent to separate from the reaction products toform a third and heaviest layer in the zone of centrifugation, the stepof maintaining a balanced hydrostatic relationship between the oil layerand the reaction products layer in the zone of centrifugation includingthe discharge of said last-mentioned layers from loci at differentdistances radially inward from the periphery of said zone; whiledischarging outwardly from the periphery of the zone of centrifugationand apart from said other layers a reagent layer as and when it forms.

6. The process of claim in which auxiliary liquid is fed into the zoneof centri-fugation.

7. The process of claim 6 in which the auxiliary liquid is of higherspecific gravity than the reaction products layer.

8. In the refining of fatty oil wherein aqueous alkaline reagent isadmixed with the oil for reaction with impurities contained therein andwherein the oil is thereafter centrifugally separated from the reactionmass in the presence of three layers in the zone of centrifugation, thelayer of lowest specific gravity comprising said oil, the layer of nexthigher specific gravity comprising reaction products, and the layer ofhighest specific gravity comprising aqueous electrolyte, the step offacilitating the maintenance of a desired hydrostatic balance betweensaid first-mentioned and second-mentioned layers in the zone ofcentrifugation by discharging said first-mew tioned layer from said zoneat a locus positioned radially inwardly from the loci of discharge ofthe other two layers, discharging said second-mentioned layer from saidzone at a locus positioned radially inwardly of the periphery of saidzone, and discharging said third-men tioned layer from the zone ofcentrifugation at the pc- 10 riphery thereof and apart from saidfirst-mentioned and said second-mentioned layers.

9. The process of claim 8 wherein the layer of highest 1 specificgravity is present in the zone of centrifugation continuously during thecentrifugal separation of the oil.

10. The process of claim 8 wherein the layer of highest specific gravityis present in the zone of centrifugat-ion intermittently during thecentrifugal separation of the oil.

11. The process of claim 8 wherein the fatty oil is vegetable oil and isrelatively low in gum content.

12. The process of claim 11 wherein the oil is relatively low in freefatty acid content.

13. The process of claim 12 wherein the alkaline reagent is sodiumhydroxide.

14. The process of claim 13 wherein the oil under treatment has beenpreviously refined with an alkaline reagent.

References Cited in the file of this patent UNITED STATES PATENTS2,412,251 Clayton Dec. 10, 1946 2,577,326 Harstick et a1. Apr. 4, 19502,717,119 Jones Sept. 6, 1955 2,759,957 Thurman Aug. 21, 1956 2,838,553Ayers et al. June 10, 1958

1. IN THE REFINING OF FATTY OIL WHEREIN AQUEOUS ALKALINE REAGENT ISADMIXED WITH THE OIL IN CONCENTRATION AND QUANTITY SUCH THAT UPONSUBJECTING THE REACTION MASS TO CENTRIFUGATION FOR THE SEPARATION OFREACTION PRODUCTS AND REAGENT FROM THE REFINED OIL THREE LAYERS AREFORMED, THE LIGHTEST LAYER BEING OF OIL, THE NEXT HEAVIER LAYER BEING OFREACTION PRODUCTS ADMIXED WITH REAGENT, AND THE HEAVIEST LAYER BEING OFREAGENT, THE STEPS WHICH COMPRISE MAINTAINING IN THE ZONE OFCENTRIFUGATION A BALANCED RELATIONSHIP BETWEEN THE OIL LAYER AND THEREACTION PRODUCT LAYER DEPENDENT UPON THEIR SPECIFIC GRAVITIES, ANDSEPARATELY DISCHARGING OUTWARDLY FROM THE PERIPHERY OF SAID ZONE OFCENTRIFUGATION THE REAGENT LAYER AS RAPIDLY AS IT IS FORMED.